Packard Forum Index » Pre-War (1899-1942)

My car starts up, runs and idles great and just "feels" like the motor is working just right. I'm getting 12-14 mpg on average, power and acceleration are all excellent.

The one issue I have periodically is, after driving for an extended while at speed in hi gear (45+ mph), upon stopping at a light and shifting back to neutral, the idle will surge up and down to the point where the engine will often quit. If I catch it in time, I can apply a quick burst of throttle and "clear it out" and it resumes it's normal idle and runs just fine again.

What could cause such an issue? I hesitate to mess with a carb that is set to deliver the great results I described in all but that one situation.

I am using non-ethanol gas with Stabil added to each tank.

It reads like you may have worn linkage which will cause the idle to be too fast or too slow depending on where it binds.

(o[]o)

A throttle linkage? How much play/slop is there supposed to be in all those bellcranks and connections?

Ideally, none. The more slop, the more prone to erratic idle speed.

(o[]o)

Uh, I wouldn't call 12-14 on a 110 excellent results. Plus your surge at idle sounds like the car is running far too rich. I surmise the float level is set too high, or the needle valve is not able to hold back the gas when the car is only idling. i.e. the level in the bowl keeps increasing till it starts to spill out into the carb throat.

Pull a spark plug and examine it. If the car is running way to rich it will be a sooty. This assumes that it is not also burning a lot of oil, in which case it would be oily and you would be able to tell.

An easy test that should take less than 5 minutes to perform.

If the throttle return spring is connected close to the carb sloppy linkage is not likely to be your issue. In addition to the carb adjustments I would look for a vacuum leak around the carb to manifold or manifold to block. This may only show up after a good warm up. The easiest way to find a vacuum leak is warm it up... Spray starter fluid all around the intake manifold gaskets. If there is a leak your engine will rev up.